KETTLEWELL, HENRY BERNARD DAVIS

evolution, ecological genetics, entomology. For the original article on Kettlewell see DSB, vol. 17.

In the years since John Turner’s original DSB entry on him, Kettlewell and his pioneering work on industrial melanism have attracted historical interest that extends well beyond its scientific merits. This interest stems from the prominent role his investigations and the phenomenon of industrial melanism have played in the teaching of biology, and the centrality of industrial melanism as an example of natural selection in creationism/intelligent design versus evolution debates. This update summarizes contemporary scientific appraisals of Kettlewell’s classic work on industrial melanism. It then discusses how legitimate scientific questions surrounding Kettlewell and his research have led popular writers and others with a fairly obvious agenda astray. A concluding section summarizes work on Kettlewell by historians and philosophers and outlines outstanding questions for further research.

In textbooks and the popular press, Kettlewell’s field experiments in the 1950s are widely portrayed as providing the first definitive evidence that industrial melanism is indeed an example of natural selection. This is inaccurate for two reasons. First, the evidence that industrial melanism in the peppered moth is an example of natural selection came from the work of geneticists who had established that the color of the peppered moth has a genetic basis (Bowater, 1914), and the observations of literally hundreds of amateur and professional collectors who documented the spread of the dark form in the vicinity of manufacturing areas during the heyday of the industrial revolution and its predictable decline owing to the passage of Clean Air legislation (Doncaster, 1906; Kettlewell, 1958; Cook, 2003; Majerus, 2005). The directional rise and fall of the dark form, not only in the peppered moth but also in literally hundreds of other species where the phenomenon is known to have occurred, definitively establishes that this is an example of natural selection (Majerus, 1998; Grant, 1999). This is true even in the absence of knowing precisely why the dark form is at an advantage in polluted environments. Kettlewell’s field experiments are considered important because they provided the first experimental demonstration that bird predation was indeed the selective mechanism at work at a time when many lepidopterists publicly doubted that bird predation was a significant factor on moth populations (e.g., Allen, 1955).

Second, although they are often depicted in the popular press as definitive, scientists have long recognized several fundamental problems in the conduct of Kettlewell’s initial field experiments (e.g., Clarke & Sheppard, 1966; Majerus, 1998; Grant, 1999). Some of these problems center around the design of his experiment, such as whether the elevated densities of moths he used to ensure his results were statistically significant might have led endemic birds to eat moths when they ordinarily do not. Other problems have been associated with the central assumptions of his investigations, such as where the moth rests by day. While industrial melanism has proven to be a more complicated phenomenon than simplistic textbook accounts would have us believe, at least eight studies since using variously modified experimental designs to get around these problems have confirmed the basic conclusions of Kettlewell’s initial experiments, namely that birds prey upon peppered moths and further that they do so differentially, depending upon how well the moth matches its background (Majerus, 2005). This being said, it seems clear further research needs to be done on the role of other nonvisual components of selection, for example, prelarval survival differences (Cook, 2000, 2003).

Sympathizers with intelligent design have misinterpreted these valid concerns about how best to interpret Kettlewell’s investigations as somehow calling into doubt whether industrial melanism is indeed an example of natural selection at all. Several have drawn attention to discrepancies between introductory textbook accounts on industrial melanism written for children and journal articles by scientists who work on the phenomenon as evidence of a conspiracy to promote evolutionary theory (e.g., Wells, 2000, but see Rudge, 2002).

Following their lead, Judith Hooper, a popular science writer, in the first book-length biography of Kettlewell, all but explicitly charges Kettlewell with committing fraud and suggests Edmund Briscoe Ford and his colleagues engaged in an elaborate coverup to prevent the truth from being widely known (Hooper, 2002). While the book captures a sense of the colorful personalities associated with what has come to be known as the “Oxford School of Ecological Genetics” (c.f. Turner, 1985, 1988, but see Cain, 1988), Hooper’s interpretation of the historical events is fundamentally flawed and rests on shoddy historical research (Rudge, 2005). Scientists familiar with research on industrial melanism have unanimously condemned the book as revealing a woeful misunderstanding of fieldwork in biology (e.g., Coyne, 2002; Grant, 2002). Much of the book is devoted to portraying Kettlewell and his associates as the sort of people who would resort to committing fraud, primarily by drawing attention to the vested interest they had in being able to provide experimental evidence for natural selection in nature.

Her implied allegation that Kettlewell committed fraud centers around a reported increase in recapture rates during his original 1953 investigation, an increase she interprets as evidence Kettlewell “fudged” his data in order to appease his boss Ford. M. Young and I. Musgrave (2005) have shown that the discrepancy upon which Hooper’s specific allegation that Kettlewell fudged his data is made is entirely explicable in the context of field studies. Numerous other interpretive problems in Hooper’s account appear to stem from a lack of field experience (Grant, 2002), poor understanding of the process of natural selection (Majerus, 2005), and a fundamentally flawed understanding of issues associated with the nature of science (Rudge, 2005). It is also unclear that Ford was as intimately involved in Kettlewell’s work as Hooper suggests (Berry, 1990).

Owen (1997) suggests Kettlewell’s published work on industrial melanism inadequately acknowledges his debt to James W. Tutt, who is generally acknowledged as the first to publish the opinion that the reason why the dark form was becoming more common near industrial sites was because of the cryptic advantage of dark coloration in soot-darkened environments (Tutt, 1890). Joel B. Hagen (1999) and David Rudge (1999) have debated whether Kettlewell’s experiment in the unpolluted wood should be interpreted as a control for the earlier experiment in a polluted setting. These papers also raise questions about how this episode has and should be depicted in science textbooks. Rudge (2003) emphasizes the role of visual imagery in accounting for why the example and Kettlewell’s

work on it has become so ubiquitous. Rudge (2000) and Douglas Allchin (2001) have also drawn attention to how this episode can and should be used to teach issues associated with the nature of science.

Several outstanding questions surround Kettlewell’s life and work that will make him the object of continued interest by historians of science. As hinted at in Turner’s original entry, Kettlewell is a fascinating individual in his own right as someone struggling to negotiate between two worlds: the world of the amateur entomologist and the world of the professional scientist. Additional work should be done to clarify the connections between his research on industrial melanism and previous research by amateur and professional scientists in Britain and other countries (briefly mentioned in Kettlewell, 1973, pp. 53–54, and Majerus, 1998). There are also outstanding questions to consider regarding whether and how his research on industrial melanism relates to his other research interests, such as his pioneering use of radioactive isotopes to track insect populations (Rudge, 2005, pp. 257–258). Further historical research on Kettlewell is also of instrumental value in making sense of the complex relationships amongst individuals associated with the Oxford School of Ecological Genetics. (The latter is a particularly important consideration given the relatively complete set of correspondence Kettlewell and Philip Sheppard left behind [archived at the Bodleian Library at Oxford University and the American Philosophical Society Library in Philadelphia respectively] compared to other individuals associated with this group, including Ford and Arthur J. Cain).

SUPPLEMENTARY BIBLIOGRAPHY

WORKS BY KETTLEWELL

“A Survey of the Frequencies of Biston betularia (L.) (Lep.) and Its Melanic Forms in Great Britain.” Heredity 12 (1958): 51–72.

The Evolution of Melanism: The Study of a Recurring Necessity. Oxford: Clarendon Press, 1973.

Clarke, C. A., and P. M. Sheppard. “A Local Survey of the Distribution of Industrial Melanic Forms in the Moth Biston betularia and Estimates of the Selective Values of These in an Industrial Environment.” Proceedings of the Royal Society of London B, Biological Science 165 (1966): 424–439.

KETTLEWELL, HENRY BERNARD DAVIS

Kettlewell was the only son of Kate Davis and of Henry Kettlewell, a merchant and member of the Corn Exchange. He was educated at Old College, Windermere, and then at the renowned English public school Charterhouse (1920–1924); studied briefly in Paris; read medicine (with zoology) at Gonville and Caius College, Cambridge, from 1926; and undertook his clinical training at St. Bartholomew’s Hospital, London, form 1929. In 1935, after graduating in medicine, he joined a general medical practice in Cranleigh, Surrey. The following year he married Hazel Margaret Wiltshire. They had a daughter who died young and a son.

During World War II Kettlewell worked for the Emergency Medical Service at the Working War Hospital. He was also for a time an anesthetist at a hospital in Guildford. With the inauguration of the National Health Service, Kettlewell left general medical practice, and in 1949 he moved to South Africa to carry out research at the International Locust Control Centre at Cape Town University, making several expeditions to the Kalahari, the Knysna Forest, the Belgian Congo, and Mozambique. In 1951 he was appointed to a senior research fellowship in the laboratory of Edmund Brisco Ford in the zoology department at Oxford, dividing his time between England and South Africa until 1954, when he was appointed senior research officer and finally settled in Oxford.

It was there that he carried out his best-known work, on the evolution of melanism in moths, over a period of two decades, leading his small research team, which sometimes included his wife and son, with great panache. Although he had the true comedian’s deep streak of sadness. Bernard Kettlewell was a big man, with a personality larger than life. Kind, charming, and irascible, he had a huge and infectious ebullience and energy, could be the life and soul of any party, and was much loved by his friends. In 1952 he returned to England by driving from Cape Town to Alexandria, surely with the same abandon with which he used to drive the English lanes. He retired in 1974 and died five years later, from an apparently accidental overdose of the medication he was using to relieve the pain of a back injury sustained during fieldwork.

Kettlewell belonged to that English tradition which sees no sharp boundary between amateur naturalist and professional biologist. As perhaps the last great exponent of that tradition, it was appropriate that he saw his work as confirming the work of its greatest exponent of all time, Charles Darwin, and that his first profession, medicine, was also Darwin’s. From his youth Kettlewell had shown an extraordinary facility for fieldwork with insects, in his teens finding species which had completely eluded experienced collectors, and later in life establishing in three days the life cycle of a rare species which had defeated a large team of enthusiasts. It was this ability which he exploited so superbly in the work he carried out at Oxford, where, at some financial loss, he converted his lifelong hobby of entomology into a profession. Theingenuity with which he could combine science and natural history was shown by his demonstration that a moth caught in his trap had migrated direct from North Africa—it was carrying a radioactive particle from a French nuclear test explosion.

Because of a long friendship with Edmund Ford, whom he had met in the Black Wood of Rannoch, a famous ecological site, in 1937, Kettlewell had agreed to join the team Ford was building up in Oxford for the “study of evolution by observation and experiment” to investigate the most spectacular and rapid evolutionary change ever witnessed; industrial melanism in moths. It was the ideal experimental situation, in which all variables but one have been manipulated into insignificance. Thenormal richness and complexity of the coadaptations of organisms with each other and with their physical environment had been almost obliterated by one overwhelming factor: the industrial and domestic soot which blanketed the more populous parts of Britain and Europe.

The extermination of the lichens that otherwise clothed the trunks of trees had left those moths which spent the day exposed there, relying only on stillness and invisibility, deprived of the camouflage they had enjoyed. Forced to rest on the soot-blackened bark, some eighty species of them had darkened during the nineteenth century. This was well enough known, and had been subjected to various neo-Lamarckian, mutationist, and (notably by J. B. S. Haldane) Darwinian interpretations, but it was Kettlewell who used it to provide spectacular evidence of the competence of natural selection to produce evolutionary change.

The two personal qualities that led to this success were Kettlewell’s great facility with insects in the field, and his status as an amateur entomologist. Although walking with the kings of population genetics, he had not lost the common touch; his knowledge of natural history and his enthusiasm for the natural history and his enthusiasm by the amateur lepidopterist, who found the work of the more rigorously trained of Kettlewell put this power to communicate with the amateur world to good effect in organizing a national survey (1952– 1970), conducted by 170 entomologists, of the distribution of the black and the lichen-patterned forms of one of the more prominent industrial melanics, the peppered moth (Biston betularia). This showed clearly that the highest frequencies of the black forms were found in the heavily polluted industrial heartlands of Britain, and that populations in the western and northern rural areas were still entirely of the lichen-camouflaged form.

By using a massive field experiment, replicated in polluted and unpolluted woodlands in 1953 and 1955, and with the help of Niko Tinbergen in observing and filming the insectivorous birds which attacked the moths during the day, Kettlewell showed that twice as many of the black form as of the pale form survived in polluted woodland, the situation being reversed in the unpolluted wood. This constituted what he described as-Darwin “missing evidence,” that evolutionary changes could be produced in natural populations through the force of natural selection acting on inheritable variation. It was a problem that could have been solved only in this way, by direct work in the field by a field naturalist. Kettlewell’s demonstration was of such elegance and simplicity as to make it one of the great classics of evolutionary biology.

During his amateur and his professional work, Kettlewell built up a large collection of Lepidoptera, rich in specimens demonstrating the genetics of melanism and other variations, which he combined with the collection of A. E. Cockayne, another medical amateur entomologist with a distinguished reputation in genetics. United with Lord Rothschild’s collection, this became the Rothschild-Cockayne-Kettlewell collection of the British Museum, a unique resource for the study of natural variation and its inheritance.

The fame his research brought him led to more popular scientific commissions: an expedition to Brazil in 1958 to commemorate the centennial of Darwin’s Origin of Species. which Kettlewell converted into a study (with a film) of insect camouflage, and a biography of Darwin (jointly with Julian Huxley), which was a pioneering example of the now standard genre of scientific biographies decorated with contemporary illustrations.

In the work that immediately followed his classic experiments, Kettlewell extended his interest to species which were melanic, and had perhaps been so for a long time, in rural rather than industrial environments: his most notable study was of Amathes (Paradiarsia) glareosa, which becomes darkened in the Shetland Isles as a result of flying in subarctic twilight against black, peaty soil. Melanism, according to his book The Evolution of Melanism, was therefore a’ recurring necessity, ’ arising in many and varied circumstances when moths were predated on a darkened background. industrial pollution providing but the latest of these. This view opened a way of comparing the coadaptation of the whole genome to genes which had been present for a long period with those that were newly arisen. This synthesis attracted relatively little attention, in part because it entailed Ronald A. Fisher’s theory of the evolution of dominance, always dear to members of Ford’s school of ecological genetics but deeply controversial among geneticists.

Although some of Kettlewell’s students extended his work to additional species, research on melanism showed signs of withering within five years of his death. Three of its best practitioners (Philip M. Sheppard, E. Robert Creed, James A. Bishop) had died young; Kettlewell’s personal style, on which the research greatly depended, was inimitable; and funding from the scientific establishment was sparse. The Royal Society declined to elect him to a fellowship, and it was significant that Kettlewell’s formal honors were all awarded in the Soviet bloc (Darwin Medal, Soviet Union, 1959; Mendel Medal, Czechoslovakia, 1965) and that in Darwin’s own country, Kettlewell had found the’ missing evidence’ not with state funds but with a grant from the privately administered Nuffield Foundation.

BIBLIOGRAPHY

1.Original Works. Kettlewell’s major book is The Evolution of Melanism: The Study of a Recurring Necessity (Oxford, 1973). The bibiography contains an extensive, but not exhaustive, compilation of his scientific papers; the preface and acknowledgments contain some autobiographical material. Kettlewell’s two more popular works are Your Book of Butterflies and Moths, which communicates clearly his enthusiasm for natural history (London, 1963), and Charles Darwin and His World (London and New York, 1965), with Julian Huxley. The chief papers describing his experiments on Biston betularia were published in Heredity: “Selection Experiments on Industrial Melanism in the Lepidoptera,” 9 (1955), 323– 342; “Further Selection Experiments on Industrial Melanism in the Lepidoptera,” 10 (1956), 287–301; and “A Survey of the Frequencies of Biston betularia L. (Lep.) and Its Melanic Forms in Britain,” 12 (1958), 51–72. For a wider audience he wrote“arwin”s Missing Evidence, ’ in Scientific American, 200 (March 1959), 48–53. His two films, later to look amateur beside the work of professional wildlife moviemakers, but pioneering classics in their day, were Evolution in Progress (cinematographer Niko Tinbergen, 1956) and Darwin and the Insects of Brazil (with the Shell Film Unit, 1958) (both distributed by British Universities Film and Video Council, London). The annotated Rothschid-Cockayne-Kettewell National Collection of British Lepidoptera is in the British Museum (Natural History), London.

II. Secondary Literature. Obituaries are Cyril A. Clarke, in Antenna, 3 no. 4 (1979), 125, and Entomologist’s Record and Journal of Variation, 91 no. 10 (1979), 253– 255; R. F. Demuth, ibid., 255–257; E. B. Ford, in Nature, 281 (1979), p. 166; and E. P. W. [Wiltshire], in Proceedings of the British Entomological and Natural History Society, 12 no. 3/4 (1979), 101–103. For a scientific review of Kettlewell’s work in context, see Edmund B. Ford, Ecological Genetics (London, 1964; 5th ed., 1975), ch. 14. A copy of the Granada TV film about about his Shetland work is held by the biology department of the University of York.

John R. G. Turner

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